20: Calculate the volume of the cuboid. 21 Measure and write down the size of angle of x. 22 Write down the special name for angle)

Length ($l$) = $5 \text{ cm}$
Width ($w$) = $4 \text{ cm}$
Height ($h$) = $2 \text{ cm}$

The volume of the cuboid is $\boxed{40 \text{ cm}^{3}}$.

21: Measure and write down the size of angle $x$
This question requires a physical measurement using a protractor. Based on visual estimation from the image, the angle $x$ appears to be an obtuse angle.
Visual estimate: $\boxed{135^\circ}$
(Note: For an accurate answer, a protractor must be used on the original paper.)

22: Write down the special name for angle $y$
The square symbol at the vertex of angle $y$ indicates that it is an angle of $90^\circ$.
The special name for an angle of $90^\circ$ is a right angle.

The special name for angle $y$ is $\boxed{\text{Right angle}}$.